The last 30 of May I had pleasure to did a Webcast together with Roberto of AvePoint. In this event we had been showing how to create a custom workflow using the new engine of SharePoint 2013. In the following image you can see a part of it.
In the following URL you can get the presentation of the Webcast
In the following URL you can get the source code in SkyDrive
In the following URL you cab get the WSP to install the solution on SharePoint 2013